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  • 301.
    Carlström, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Garaud, Julien
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Length scales, collective modes, and type-1.5 regimes in three-band superconductors2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 13, p. 134518-Article in journal (Refereed)
    Abstract [en]

    The recent discovery of iron pnictide superconductors has resulted in a rapidly growing interest in multiband models with more than two bands. In this work we specifically focus on the properties of three-band Ginzburg-Landau models which do not have direct counterparts in more studied two-band models. First we derive normal modes and characteristic length scales in the conventional U(1) three-band Ginzburg-Landau model as well as in its time-reversal symmetry-broken counterpart with U(1) x Z(2) symmetry. We show that, in the latter case, the normal modes are mixed phase-density collective excitations. A possibility of the appearance of a massless mode associated with fluctuations of the phase difference is also discussed. Next we show that gradients of densities and phase differences can be inextricably intertwined in vortex excitations in three-band models. This can lead to very long-range attractive intervortex interactions and the appearance of type-1.5 regimes even when the intercomponent Josephson coupling is large. In some cases it also results in the formation of a domainlike structure in the form of a ring of suppressed density around a vortex across which one of the phases shifts by p. We also show that field-induced vortices can lead to a change of broken symmetry from U(1) to U(1) x Z(2) in the system. In the type-1.5 regime, it results in a semi-Meissner state where the system has a macroscopic phase separation in domains with broken U(1) and U(1) x Z(2) symmetries.

  • 302.
    Carlström, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Garaud, Julien
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Semi-Meissner state and nonpairwise intervortex interactions in type-1.5 superconductors2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 13, p. 134515-Article in journal (Refereed)
    Abstract [en]

    We demonstrate the existence of nonpairwise interaction forces between vortices in multicomponent and layered superconducting systems. That is, in contrast to most common models, the interaction in a group of such vortices is not a universal superposition of Coulomb or Yukawa forces. Next, we consider the properties of vortex clusters in a semi-Meissner state of type-1.5 two-component superconductors. We show that under certain conditions nonpairwise forces can contribute to the formation of very complex vortex states in type-1.5 regimes.

  • 303. Carniato, S.
    et al.
    Dufour, G.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    Ab initio study of the Cu 2p and 3s core-level XPS spectra of copper phthalocyanine2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 4Article in journal (Refereed)
    Abstract [en]

    The x-ray photoelectron spectra (XPS) of copper tetraazaporphyrin (CuTAP), used as a model of copper phthalocyanine(CuPc) are studied by theoretical simulations. The nature of the main and satellite features observed in the XPS Cu 2p and Cu 3s photoelectron spectra are discussed based on the results of the charge-transfer (CT) model and of ab initio calculations in the sudden approximation limit. It is shown that the two descriptions of the core level final states can be derived from the two types of approaches. The final-state wave functions given by the CT model are described in a shakedown scenario. This process produces a well-screened final 2p(5)3d(10)(L) under bar configuration ((L) under bar denotes a ligand hole) on the Cu atom together with the core hole, resulting in the main spectral peak. On the other hand, the process where the outer electron stays on the ligand corresponds to the satellite with a poorly-screened 2p(5)3d(9) character. The ab initio calculations, performed on an isolated copper tetraazaporphyrin molecule at the Hartree-Fock (HF) level, the multi-configuration self-consistent field level, and the hybrid density-functional-theory levels show that the core hole final states (satellite/main peak) can be attributed to valence-valence transitions. We show that a correct intensity distribution of the different features, including the so-called white line and the satellite structures, can be obtained when the electronic relaxation and correlation and the overlap between the ground-state and final-state Slater determinants are explicitly taken into account. It is found that the nature of the main peak is strongly depending on the Ligand-to-Metal charge transfer, on the exchange interaction and on the core-hole-3d-hole interaction energies.

  • 304.
    Caron, L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Hudl, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Höglin, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Dung, N. H.
    Gómez, Cesar Pay
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Bruck, E.
    Andersson, Yvonne
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetocrystalline anisotropy and the magnetocaloric effect in Fe2P2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 9, p. 094440-Article in journal (Refereed)
    Abstract [en]

    Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a moderate magnetic entropy change, which spans over 70 K and the presence of strong magnetization anisotropy proves this system is not fully itinerant but displays a mix of itinerant and localized magnetism. The properties of pure Fe2P are compared to those of giant magnetocaloric (Fe,Mn)2(P,A) (where A = As, Ge, Si) compounds helping understand the exceptional characteristics shown by the latter, which are so promising for heat pump and energy conversion applications.

  • 305.
    Caron, Luana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Trung, N T
    Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, TU Delft, Nederländerna.
    Brück, E
    Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, TU Delft, Nederländerna.
    Pressure-tuned magnetocaloric effect in Mn(0.93)Cr(0.07)CoGe2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 2, p. 020414-Article in journal (Refereed)
    Abstract [en]

    Effects of physical and chemical pressures in the Mn(1-x)Cr(x)CoGe series of compounds are studied. Cr substitution and hydrostatic pressure play similar roles in displacing T(C) to lower temperatures and coupling or decoupling magnetic and crystallographic transitions. In this work the similarities and differences between the effects of chemical and physical pressures are explored, helping unveil the nature of the first-order phase transition presented by MnCoGe-based compounds.

  • 306.
    Carva, K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Turek, I
    Landauer theory of ballistic torkances in noncollinear spin valves2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 10, p. 104432-Article in journal (Refereed)
    Abstract [en]

    We present a theory of voltage-induced spin-transfer torques in ballistic noncollinear spin valves. The torkance on one ferromagnetic layer is expressed in terms of scattering coefficients of the whole spin valve, in analogy to the Landauer conductance formula. The theory is applied to Co/Cu/Ni(001)-based systems where long-range oscillations of the Ni torkance as a function of Ni thickness are predicted. The oscillations represent a novel quantum size effect due to the noncollinear magnetic structure. The oscillatory behavior of the torkance contrasts a thickness-independent trend of the conductance.

  • 307. Carva, Karel
    et al.
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Legut, D.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio theory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 18, p. 184425-Article in journal (Refereed)
    Abstract [en]

    We report a computational theoretical investigation of electron spin-flip scattering induced by the electron-phonon interaction in the transition-metal ferromagnets bcc Fe, fcc Co, and fcc Ni. The Elliott-Yafet electron-phonon spin-flip scattering is computed from first principles, employing a generalized spin-flip Eliashberg function as well as ab initio computed phonon dispersions. Aiming at investigating the amount of electron-phonon mediated demagnetization in femtosecond laser-excited ferromagnets, the formalism is extended to treat laser-created thermalized as well as nonequilibrium, nonthermal hot electron distributions. Using the developed formalism we compute the phonon-induced spin lifetimes of hot electrons in Fe, Co, and Ni. The electron-phonon mediated demagnetization rate is evaluated for laser-created thermalized and nonequilibrium electron distributions. Nonthermal distributions are found to lead to a stronger demagnetization rate than hot, thermalized distributions, yet their demagnetizing effect is not enough to explain the experimentally observed demagnetization occurring in the subpicosecond regime.

  • 308.
    Carva, Karel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplap
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Defect-controlled electronic transport in single, bilayer, and N-doped graphene: Theory2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 24, p. 245405-Article in journal (Refereed)
    Abstract [en]

    We report on a theoretical study of the electronic-structure and transport properties of single and bilayer graphene with vacancy defects, as well as N-doped graphene. The theory is based on first-principles calculations as well as model investigations in terms of real-space Green's functions. We show that increasing the defect concentration increases drastically the conductivity in the limit of zero applied gate voltage, by establishing carriers in originally carrier-free graphene, a fact which is in agreement with recent observations. We calculate the amount of defects needed for a transition from a nonconducting to a conducting regime (i.e., a metal-insulator transition) and establish the threshold of the defect concentration where the increase in impurity scattering dominates over the increase in carrier-induced conductivity.

  • 309.
    Carvahlo, A.
    et al.
    Department of Physics, I3N, University of Aveiro, Campus Santiago.
    Coutinho, J.
    Department of Physics, I3N, University of Aveiro, Campus Santiago.
    Barroso, M.
    Department of Physics, I3N, University of Aveiro, Campus Santiago.
    Silva, E.L.
    Department of Physics, CEMDRX and CFC, Faculty of Science and Technology, University of Coimbra.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Electronic structure modification of Si nanocrystals with F(4)-TCNQ2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 12Article in journal (Refereed)
    Abstract [en]

    We use first-principles models to demonstrate how an organic oxidizing agent F(4)-TCNQ (7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane) modifies the electronic structure of silicon nanocrystals, suggesting it may enhance p-type carrier density and mobility. The proximity of the lowest unoccupied level of F(4)-TCNQ to the highest occupied level of the Si nanocrystals leads to the formation of an empty hybrid state overlapping both the nanocrystal and molecule, reducing the excitation energy to similar to 0.8-1 eV in vacuum. Hence, it is suggested that F(4)-TCNQ can serve both as a surface oxidant and as a mediator for hole hopping between adjacent nanocrystals in p-type doped silicon nanocrystal networks

  • 310.
    Carvahlo, A.
    et al.
    School of Physics, University of Exeter.
    Tagantsev, A.K.
    Ceramics Laboratory, Swiss Federal Institute of Technology (EPFL), Lausanne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    School of Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Setter, N.
    Ceramics Laboratory, Swiss Federal Institute of Technology (EPFL), Lausanne.
    Cation-site intrinsic defects in Zn-doped CdTe2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 7, p. 75215-Article in journal (Refereed)
    Abstract [en]

    The properties of the cation vacancy and the Te antisite, two dominant defects in CdTe and Cd1-xZnxTe alloys grown in Te-rich conditions, are examined using first-principles calculations. First, the structure, electronic levels, and migration paths of V-Cd and Te-Cd in CdTe are studied in detail. Additionally, we analyze the evolution of the stability and electronic properties in Cd1-xZnxTe alloys, taking into account both the role of alloying in the position of the ionization levels and its effects on the equilibrium concentration of those two defects. It is shown that the formation of cation vacancies becomes progressively more favorable as x increases, whereas Te antisites become less stable, backing the trend towards p-type conductivity in dilute Cd1-xZnxTe.

  • 311.
    Carvahlo, A.
    et al.
    Department of Physics, I3N, University of Aveiro, Campus Santiago.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Electronic properties, doping, and defects in chlorinated silicon nanocrystals2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 4Article in journal (Refereed)
    Abstract [en]

    Silicon nanocrystals with diameters between 1 and 3 nm and surfaces passivated by chlorine or a mixture of chlorine and hydrogen were modeled using density functional theory, and their properties compared with those of fully hydrogenated nanocrystals. It is found that fully and partially chlorinated nanocrystals are stable, and have higher electron affinity, higher ionization energy, and lower optical absorption energy threshold. As the hydrogenated silicon nanocrystals, chlorinated silicon nanocrystals doped with phosphorus or boron require a high activation energy to transfer an electron or hole, respectively, to undoped silicon nanocrystals. The electronic levels of surface dangling bonds are similar for both types of surface passivation, although in the chlorinated silicon nanocrystals some fall outside the narrower energy gap.

  • 312.
    Carvalho, A.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Coutinho, J.
    University of Aveiro.
    Torres, V. J. B.
    University of Aveiro.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Alsina, J. M. Campanera
    University of Sussex.
    Shaw, M.
    University of Newcastle Upon Tyne.
    Briddon, P. R.
    University of Newcastle Upon Tyne.
    Local-density-functional calculations of the vacancy-oxygen center in Ge2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 11Article in journal (Refereed)
    Abstract [en]

    We carry out a comprehensive density-functional study of the vacancy-oxygen (VO) center in germanium using large H-terminated Ge clusters. The importance of a nonlinear core correction to account for the involvement of the 3d electrons in Ge-O bonds is discussed. We calculate the electrical levels and the vibrational modes of VO0, VO-, and VO= finding close agreement with experiment. We also explore the reorientation, migration, and dissociation mechanisms of neutral and negatively charged VO and compare the calculated energy barriers with experimental data. We conclude that the defect is likely to anneal through both mechanisms.

  • 313. Castleton, C. W. M.
    et al.
    Höglund, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Goethelid, M.
    Qian, M. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Mirbt, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hydrogen on III-V (110) surfaces: Charge accumulation and STM signatures2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 4, p. 045319-Article in journal (Refereed)
    Abstract [en]

    The behavior of hydrogen on the 110 surfaces of III-V semiconductors is examined using ab initio density functional theory. It is confirmed that adsorbed hydrogen should lead to a charge accumulation layer in the case of InAs, but shown here that it should not do so for other related III-V semiconductors. It is shown that the hydrogen levels due to surface adsorbed hydrogen behave in a material dependent manner related to the ionicity of the material, and hence do not line up in the universal manner reported by others for hydrogen in the bulk of semiconductors and insulators. This fact, combined with the unusually deep Gamma point conduction band well of InAs, accounts for the occurrence of an accumulation layer on InAs(110) but not elsewhere. Furthermore, it is shown that adsorbed hydrogen should be extremely hard to distinguish from native defects (particularly vacancies) using scanning tunneling and atomic force microscopy, on both InAs(110) and other III-V (110) surfaces.

  • 314. Castleton, C. W. M.
    et al.
    Höglund, A.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Qian, M. C.
    Mirbt, S.
    Hydrogen on III-V (110) surfaces: Charge accumulation and STM signatures2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 4, p. 045319-Article in journal (Refereed)
    Abstract [en]

    The behavior of hydrogen on the 110 surfaces of III-V semiconductors is examined using ab initio density functional theory. It is confirmed that adsorbed hydrogen should lead to a charge accumulation layer in the case of InAs, but shown here that it should not do so for other related III-V semiconductors. It is shown that the hydrogen levels due to surface adsorbed hydrogen behave in a material dependent manner related to the ionicity of the material, and hence do not line up in the universal manner reported by others for hydrogen in the bulk of semiconductors and insulators. This fact, combined with the unusually deep Gamma point conduction band well of InAs, accounts for the occurrence of an accumulation layer on InAs(110) but not elsewhere. Furthermore, it is shown that adsorbed hydrogen should be extremely hard to distinguish from native defects (particularly vacancies) using scanning tunneling and atomic force microscopy, on both InAs(110) and other III-V (110) surfaces.

  • 315.
    Castleton, C W M
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Mirbt, S
    Finite-size scaling as a cure for supercell approximation errors in calculations of neutral native defects in InP2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 19, p. 195202-Article in journal (Refereed)
    Abstract [en]

    The relaxed and unrelaxed formation energies of neutral antisites and interstitial defects in InP are calculated using ab initio density functional theory and simple cubic supercells of up to 512 atoms. The finite-size errors in the formation energies of all the neutral defects arising from the supercell approximation are examined and corrected for using finite-size scaling methods, which are shown to be a very promising approach to the problem. Elastic errors scale linearly, while the errors arising from charge multipole interactions between the defect and its images in the periodic boundary conditions have a linear plus a higher order term, for which a cubic provides the best fit. These latter errors are shown to be significant even for neutral defects. Instances are also presented where even the 512 atom supercell is not sufficiently converged. Instead, physically relevant results can be obtained only by finite-size scaling the results of calculations in several supercells, up to and including the 512 atom cell and in extreme cases possibly even including the 1000 atom supercell.

  • 316.
    Castleton, C W M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Mirbt, S
    Finite-size scaling as a cure for supercell approximation errors in calculations of neutral native defects in InP2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 19, p. 195202-Article in journal (Refereed)
    Abstract [en]

    The relaxed and unrelaxed formation energies of neutral antisites and interstitial defects in InP are calculated using ab initio density functional theory and simple cubic supercells of up to 512 atoms. The finite-size errors in the formation energies of all the neutral defects arising from the supercell approximation are examined and corrected for using finite-size scaling methods, which are shown to be a very promising approach to the problem. Elastic errors scale linearly, while the errors arising from charge multipole interactions between the defect and its images in the periodic boundary conditions have a linear plus a higher order term, for which a cubic provides the best fit. These latter errors are shown to be significant even for neutral defects. Instances are also presented where even the 512 atom supercell is not sufficiently converged. Instead, physically relevant results can be obtained only by finite-size scaling the results of calculations in several supercells, up to and including the 512 atom cell and in extreme cases possibly even including the 1000 atom supercell.

  • 317.
    Castleton, Christopher W. M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Höglund, A.
    Mirbt, S.
    Managing the supercell approximation for charged defects in semiconductors: Finite-size scaling, charge correction factors, the band-gap problem, and the ab initio dielectric constant2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 3, p. 035215-Article in journal (Refereed)
    Abstract [en]

    The errors arising in ab initio density functional theory studies of semiconductor point defects using the supercell approximation are analyzed. It is demonstrated that (a) the leading finite size errors are inverse linear and inverse cubic in the supercell size and (b) finite size scaling over a series of supercells gives reliable isolated charged defect formation energies to around +/- 0.05 eV. The scaled results are used to test three correction methods. The Makov-Payne method is insufficient, but combined with the scaling parameters yields an ab initio dielectric constant of 11.6 +/- 4.1 for InP. Gamma point corrections for defect level dispersion are completely incorrect, even for shallow levels, but realigning the total potential in real-space between defect and bulk cells actually corrects the electrostatic defect-defect interaction errors as well. Isolated defect energies to +/- 0.1 eV are then obtained using a 64 atom supercell, though this does not improve for larger cells. Finally, finite size scaling of known dopant levels shows how to treat the band gap problem: in <= 200 atom supercells with no corrections, continuing to consider levels into the theoretical conduction band (extended gap) comes closest to experiment. However, for larger cells or when supercell approximation errors are removed, a scissors scheme stretching the theoretical band gap onto the experimental one is in fact correct.

  • 318.
    Castleton, CWM
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Höglund, A
    Theory of Condensed Matter, Department of Physics, Uppsala University, Uppsala.
    Mirbt, S
    Theory of Condensed Matter, Department of Physics, Uppsala University, Uppsala.
    Managing the supercell approximation for charged defects in semiconductors: Finite-size scaling, charge correction factors, the band-gap problem, and the ab initio dielectric constant2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 3, article id 035215Article in journal (Refereed)
    Abstract [en]

    The errors arising in ab initio density functional theory studies of semiconductor point defects using the supercell approximation are analyzed. It is demonstrated that (a) the leading finite size errors are inverse linear and inverse cubic in the supercell size and (b) finite size scaling over a series of supercells gives reliable isolated charged defect formation energies to around +/- 0.05 eV. The scaled results are used to test three correction methods. The Makov-Payne method is insufficient, but combined with the scaling parameters yields an ab initio dielectric constant of 11.6 +/- 4.1 for InP. Gamma point corrections for defect level dispersion are completely incorrect, even for shallow levels, but realigning the total potential in real-space between defect and bulk cells actually corrects the electrostatic defect-defect interaction errors as well. Isolated defect energies to +/- 0.1 eV are then obtained using a 64 atom supercell, though this does not improve for larger cells. Finally, finite size scaling of known dopant levels shows how to treat the band gap problem: in <= 200 atom supercells with no corrections, continuing to consider levels into the theoretical conduction band (extended gap) comes closest to experiment. However, for larger cells or when supercell approximation errors are removed, a scissors scheme stretching the theoretical band gap onto the experimental one is in fact correct.

  • 319.
    Cava, Carlos Eduardo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Roman, Lucimara Stolz
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Effects of native defects on the structural and magnetic properties of hematite alpha-Fe2O32013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 4, p. 045136-Article in journal (Refereed)
    Abstract [en]

    Antiferromagnetic and ferromagnetic configurations of hematite alpha-Fe2O3 structures have been investigated by first-principles methods, which have been used to theoretically analyze the local structural and magnetic effects due to the presence of interstitial atoms such as hydrogen and oxygen. This study is based on the projector-augmented wave method within the local spin density approximation (LSDA) in addition to an on-site Coulomb correction of the Fe d orbitals (i.e., the LSDA + U-SIC method). The results demonstrate that this correction potential is important in achieving an accurate description of both the structural and the magnetic properties of alpha-Fe2O3. The ground state of alpha-Fe2O3 is the antiferromagnetic phase. The presence of oxygen vacancies, interstitial oxygen, and an interstitial hydrogen decreases the local Fe magnetic moment vertical bar M-s(Fe)vertical bar in both the ferro- and antiferromagnetic phases, although the hydrogen has a rather modest effect. The density of states calculations demonstrate that the presence of interstitial atoms and defects yields a small reduction in the material's electronic gap.

  • 320. Cehovin, Alexander
    et al.
    Canali, Carlo M.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    H. MacDonald, Allan
    Elementary Excitations of Ferromagnetic Metal Nanoparticles2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 1, p. 144231-1442317Article in journal (Refereed)
  • 321. Cehovin, Alexander
    et al.
    Canali, Carlo M.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    H. MacDonald, Allan
    Magnetization orientation dependence of the quasiparticle and hysteresis in ferromagnetic metal nanoparticles2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 9, p. 944301-9443015Article in journal (Refereed)
  • 322. Cehovin, Alexander
    et al.
    Canali, Carlo M.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    MacDonald, Allan
    Orbital and Spin Contributions to the g-Tensors in Metal Nanoparticles2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 4, p. 454111-8-45411-8Article in journal (Refereed)
  • 323. Chakraborty, P. B.
    et al.
    Henelius, Patrik
    KTH, Superseded Departments, Physics.
    Kjonsberg, H.
    Sandvik, A. W.
    Girvin, S. M.
    Theory of the magnetic phase diagram of LiHoF42004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 14Article in journal (Refereed)
    Abstract [en]

    The properties of LiHoF4 are believed to be well described by a long-range dipolar Ising model. We go beyond mean-field theory and calculate the phase diagram of the Ising model in a transverse field using a quantum Monte Carlo method. The relevant Ising degrees of freedom are obtained using a nonperturbative projection onto the low-lying crystal-field eigenstates. We explicitly take the domain structure into account, and the strength of the near-neighbor exchange interaction is obtained as a fitting parameter. The on-site hyperfine interaction is approximately taken into account through a renormalization of the transverse applied magnetic field. Finally, we propose a spectroscopy experiment to precisely measure the most important parameter controlling the location of the phase boundary.

  • 324.
    Chang, Johan
    et al.
    Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen.
    Pailhés, Stephane
    Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen.
    Shi, Ming
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Voigt, Jörg
    Institute for Solid State Research, Forschungszentrum Jülich.
    Perez, V.
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Patthey, Luc
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Momono, Naoki
    Department of Physics, Hokkaido University, Sapporo.
    Oda, Migaku
    Department of Physics, Hokkaido University, Sapporo.
    Ido, Masayuki
    Department of Physics, Hokkaido University, Sapporo.
    Schnyder, A.
    Condensed Matter Theory Group, Villigen.
    Mudry, C.
    Condensed Matter Theory Group, Villigen.
    Mesot, Joël
    Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, Villigen.
    When low- and high-energy electronic responses meet in cuprate superconductors2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 22, p. 224508-Article in journal (Refereed)
    Abstract [en]

    The existence of coherent quasiparticles near the Fermi energy in the low-temperature state of high-temperature superconductors has been well established by angle-resolved photoemission spectroscopy (ARPES). We present a study of La1.83Sr0.17CuO4 in the superconducting state and report an abrupt change in the quasiparticle spectral function, as we follow the dispersion of the ARPES signal from the Fermi energy to 0.6 eV. The interruption in the quasiparticle dispersion separates coherent quasiparticle peaks at low energies from broad incoherent excitations at high energies. We find that the boundary between these low-energy and high-energy features exhibits a cosine-shaped momentum dependence, reminiscent of the superconducting d-wave gap. Further intriguing similarities between characteristics of the incoherent excitations and quasiparticle properties suggest a close relation between the electronic response at high and low energies in cuprate superconductors.

  • 325.
    Chang, Johan
    et al.
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Shi, Ming
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Pailhés, Stephane
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Månsson, Martin
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Claesson, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Bendounan, Azzedin
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Sassa, Yasmine
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Patthey, Luc
    Swiss Light Source, Paul Scherrer Institute, Villigen.
    Momono, Naoki
    Department of Physics, Hokkaido University, Sapporo.
    Oda, Migaku
    Department of Physics, Hokkaido University, Sapporo.
    Ido, Masayuki
    Department of Physics, Hokkaido University, Sapporo.
    Guerrero, S.
    Condensed Matter Theory Group, Paul Scherrer Institute, Villigen.
    Mudry, C.
    Condensed Matter Theory Group, Paul Scherrer Institute, Villigen.
    Mesot, Joël
    Laboratory for Neutron Scattering, ETH Zurich, Paul Scherrer Institute, Villigen.
    Anisotropic quasiparticle scattering rates in slightly underdoped to optimally doped high-temperature La2-xSrxCuO4 superconductors2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 20, p. 205103-Article in journal (Refereed)
    Abstract [en]

    An angle-resolved photoemission study of the scattering rate in the superconducting phase of the high-temperature superconductor La2-xSrxCuO4 with x=0.145 and x=0.17, as a function of binding energy and momentum, is presented. We observe that the scattering rate scales linearly with binding energy up to the high-energy scale E-1 similar to 0.4 eV. The scattering rate is found to be strongly anisotropic, with a minimum along the (0,0)-(pi,pi) direction. A possible connection to a quantum-critical point is discussed.

  • 326. Chantis, Athanasios N.
    et al.
    Smith, L
    Fransson, J
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Balatsky, A. V.
    Scanning tunneling microscopy detection of spin polarized resonant surface bands: The example of Fe(001)2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 16, p. 165423-Article in journal (Refereed)
    Abstract [en]

    We study theoretically the effect of a spin polarized resonant surface band on the conductance of scanning tunneling spectroscope with a spin polarized tip (SP-STM). Using the example of the Fe(001) surface, we show that a minority-spin surface state can induce a bias dependence of the tunneling differential conductance which depends strongly on the orientation of the magnetization in the SP-STM tip relative to the magnetization axis in the surface. We propose the use of this effect to determine the spin character of the surface band.

  • 327. Chaparro, C.
    et al.
    Fang, L.
    Claus, H.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Crabtree, G. W.
    Stanev, V.
    Kwok, W. K.
    Welp, U.
    Doping dependence of the specific heat of single crystal bafe2(as1 xpx)(2)2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 18, p. 184525-Article in journal (Refereed)
    Abstract [en]

    We present specific heat measurements on a series of BaFe2(As1-xPx)(2) single crystals with phosphorous doping ranging from x = 0.3 to x = 0.55. Our results reveal that BaFe2(As1-xPx)(2) follows the scaling Delta C/T-c approximate to T-c(2) remarkably well. The clean-limit nature of this material imposes additional restraints on theories aimed at explaining the scaling. Furthermore, we find that the Ginzburg-Landau parameter decreases significantly with doping whereas the superconducting anisotropy is Gamma approximate to 2.6, independent of doping.

  • 328.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Slowdown of light due to exciton-polariton propagation in ZnO2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 24, p. 245212-Article in journal (Refereed)
    Abstract [en]

    By employing time-of-flight spectroscopy, the group velocity of light propagating through bulk ZnO is demonstrated to dramatically decrease down to 2044 km/s when photon energy approaches the absorption edge of the material. The magnitude of this decrease is found to depend on light polarization. It is concluded that even though the slowdown is observed in the vicinity of donor bound exciton (BX) resonances, the effect is chiefly governed by dispersion of free exciton (FX) polaritons that propagate coherently via ballistic transport. Based on the experimentally determined spectral dependence of the polariton group velocity, the polariton dispersion is accurately determined.

  • 329.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Spin dynamics of isoelectronic bound excitons in ZnO2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 23, p. 235202-Article in journal (Refereed)
    Abstract [en]

    Time-resolved optical spin orientation is employed to study spin dynamics of I * and I-1* excitons bound to isoelectronic centers in bulk ZnO. It is found that spin orientation at the exciton ground state can be generated using resonant excitation via a higher lying exciton state located at about 4 meV from the ground state. Based on the performed rate equation analysis of the measured spin dynamics, characteristic times of subsequent hole, electron, and direct exciton spin flips in the exciton ground state are determined as being tau(s)(h) = 0.4 ns, tau(s)(e) greater than= 15 ns, and tau(s)(eh) greater than= 15 ns, respectively. This relatively slow spin relaxation of the isoelectronic bound excitons is attributed to combined effects of (i) weak e-h exchange interaction, (ii) restriction of the exciton movement due to its binding at the isoelectronic center, and (iii) suppressed spin-orbit coupling for the tightly bound hole.

  • 330.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Zeeman splitting and dynamics of an isoelectronic bound exciton near the band edge of ZnO2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 23Article in journal (Refereed)
    Abstract [en]

    Comprehensive time-resolved photoluminescence and magneto-optical measurements are performed on a bound exciton (BX) line peaking at 3.3621 eV (labeled as I*). Though the energy position of I* lies within the same energy range as that for donor bound exciton (DX) transitions, its behavior in an applied magnetic field is found to be distinctly different from that observed for DXs bound to either ionized or neutral donors. An exciton bound to an isoelectronic center with a hole-attractive local potential is shown to provide a satisfactory model that can account for all experimental results of the I* transition. DOI: 10.1103/PhysRevB.86.235205

  • 331.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Rudko, GY
    Mal'shukov, AG
    Chao, KA
    Toropov, AA
    Terent'ev, Y
    Sorokin, SV
    Lebedev, Alexander
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Ivanov, SV
    Kop'ev, PS
    Exciton spin relaxation in diluted magnetic semiconductor Zn1-xMnxSe/CdSe superlattices: Effect of spin splitting and role of longitudinal optical phonons2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 12Article in journal (Refereed)
    Abstract [en]

    Exciton spin relaxation in diluted magnetic semiconductor (DMS) structures based on ZnMnSe is closely examined as a function of exciton spin splitting in an external magnetic field. A drastic increase in spin relaxation is observed when exciton spin splitting exceeds the longitudinal optical (LO) phonon energy. Direct experimental evidence has been provided from (1) spin injection from the DMS to an adjacent nonmagnetic quantum well that can be modulated by the LO-assisted spin relaxation and (2) hot exciton photoluminescence within the DMS where a spin flip is accompanied by the emission of one LO phonon.

  • 332.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kayanuma, K.
    Nishibayashi, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Toropov, A.A.
    Lebedev, A.V.
    Sorokin, S.V.
    Identification of a dominant mechanism for optical spin injection from a diluted magnetic semiconductor: Spin-conserving energy transfer via localized excitations2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 7, p. 73206-Article in journal (Refereed)
    Abstract [en]

    We provide compelling experimental evidence for a spin-conserving energy-transfer process via localized excitations as being responsible for the observed optical spin injection in ZnMnSe ZnCdSe quantum structures. We show that such a process is common and inherent to a diluted magnetic semiconductor because of strong potential fluctuations. © 2005 The American Physical Society.

  • 333. Cheng, Benyuan
    et al.
    Li, Quanjun
    Zhang, Huafang
    Liu, Ran
    Liu, Bo
    Yao, Zhen
    Cui, Tian
    Liu, Jing
    Liu, Zhenxian
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Superhard Materials, Jilin University, 130012 Changchun, China.
    Liu, Bingbing
    Pressure-induced metallization and amorphization in VO2(A) nanorods2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, no 18, article id 184109Article in journal (Refereed)
    Abstract [en]

    A metallic state enabled by the metal-insulator transition (MIT) in single crystal VO2(A) nanorods is demonstrated, which provides important physical foundation in experimental understanding of MIT in VO2. The observed tetragonal metallic state at ∼28 GPa should be interpreted as a distinct metastable state, while increasing pressure to ∼32 GPa, it transforms into a metallic amorphous state completely. The metallization is due to V 3d orbital electrons delocalization, and the amorphization is attributed to the unique variation of V-O-V bond angle. A metallic amorphous VO2 state is found under pressure, which is beneficial to explore the phase diagram of VO2. Furthermore, this work proves the occurrence of both the metallization and amorphization in octahedrally coordinated materials.

  • 334. Cherian, R.
    et al.
    Mahadevan, P.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Trends in ferromagnetism in Mn-doped dilute III-V alloys from a density functional perspective2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 19Article in journal (Refereed)
    Abstract [en]

    Mn doping in dilute III-V alloys has been examined as a route to enhance ferromagnetic stability. Strong valence-band bowing is expected at the dilute limit, implying a strong modification of the ferromagnetic stability upon alloying with even an increase in some cases. Using first-principles electronic structure calculations we show that while codoping with a group V anion enhances the ferromagnetic stability in some cases when the effects of relaxation of the lattice are not considered, strong impurity scattering in the relaxed structure result in a reduction in the ferromagnetic stability.

  • 335.
    Chevrier, Vincent L.
    et al.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Ong, Shyue P.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Armiento, Rickard
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Chan, Maria K. Y.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Ceder, Gerbrand
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Hybrid density functional calculations of redox potentials and formation energies of transition metal compounds2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 7, p. 075122-Article in journal (Refereed)
    Abstract [en]

    We compare the accuracy of conventional semilocal density functional theory (DFT), the DFT+U method, and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for structural parameters, redox reaction energies, and formation energies of transition metal compounds. Conventional DFT functionals significantly underestimate redox potentials for these compounds. Zhou et al. [Phys. Rev. B 70, 235121 (2004)] addressed this issue with DFT+U and a linear-response scheme for calculating U values. We show that the Li intercalation potentials of prominent Li-ion intercalation battery materials, such as the layered Li(x)MO(2) (M=Co and Ni), Li(x)TiS(2); olivine Li(x)MPO(4) (M=Mn, Fe, Co, and Ni); and spinel-like Li(x)Mn(2)O(4), Li(x)Ti(2)O(4), are also well reproduced by HSE06, due to the self-interaction error correction from the partial inclusion of Hartree-Fock exchange. For formation energies, HSE06 performs well for transition metal compounds, which typically are not well reproduced by conventional DFT functionals but does not significantly improve the results of nontransition metal oxides. Hence, we find that hybrid functionals provide a good alternative to DFT+U for transition metal applications when the large extra computational effort is compensated by the benefits of (i) avoiding species-specific adjustable parameters and (ii) a more universal treatment of the self-interaction error that is not exclusive to specific atomic orbital projections on selected ions.

  • 336. Chia, Han-Jong
    et al.
    Guo, Feng
    Belova, Liubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    McMichael, R. D.
    Two-dimensional spectroscopic imaging of individual ferromagnetic nanostripes2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 18, p. 184406-Article in journal (Refereed)
    Abstract [en]

    We use ferromagnetic-resonance force microscopy to spectroscopically image the edge modes in individual 700 nm and 400 nm wide Permalloy stripes with a spatial resolution on the order of 200 nm. The imaging clearly identifies some resonances as edge modes in stripes in a case where mode identification by comparison with micromagnetic modeling is not clear. Combined spectroscopic and spatial scans reveal clear differences in the edge mode resonances at opposite edges of the stripes as well as inhomogeneity along the length of the stripe.

  • 337.
    Chico, Jonathan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Etz, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thermally driven domain-wall motion in Fe on W(110)2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 1, p. 014434-Article in journal (Refereed)
    Abstract [en]

    It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange.

  • 338. Chico, Jonathan
    et al.
    Etz, Corina
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Eriksson, Olle
    Fransson, Jonas
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala Univ, Sweden.
    Bergman, Anders
    Thermally driven domain-wall motion in Fe on W(110)2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 1, p. 014434-Article in journal (Refereed)
    Abstract [en]

    It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange.

  • 339.
    Chico, Jonathan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Keshavarz, Samara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Etz, Corina
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    First principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, no 21, article id 214439Article in journal (Refereed)
    Abstract [en]

    Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fact that some Heusler alloys are half-metallic. In the following, a systematic study of the magnetic properties of three different Heusler families Co(2)MnZ, Co(2)FeZ, and Mn(2)VZ with Z = (Al, Si, Ga, Ge) is performed. A key aspect is the determination of the Gilbert damping from first-principles calculations, with special focus on the role played by different approximations, the effect that substitutional disorder and temperature effects. Heisenberg exchange interactions and critical temperature for the alloys are also calculated as well as magnon dispersion relations for representative systems, the ferromagnetic Co2FeSi and the ferrimagnetic Mn2VAl. Correlation effects beyond standard density-functional theory are treated using both the local spin density approximation including the Hubbard U and the local spin density approximation plus dynamical mean field theory approximation, which allows one to determine if dynamical self-energy corrections can remedy some of the inconsistencies which were previously reported for these alloys.

  • 340.
    Chimata, Raghuveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Isaeva, Leyla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kadas, Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mentink, Johan H.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Katsnelson, Mikhail I.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Rasing, Theo
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Kirilyuk, Andrei
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Kimel, Alexey
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 9, article id 094411Article in journal (Refereed)
    Abstract [en]

    In recent years there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e., first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbor exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

  • 341. Chioncel, L.
    et al.
    Benea, D.
    Ebert, H.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Minar, J.
    Momentum space anisotropy of electronic correlations in Fe and Ni: An analysis of magnetic Compton profiles2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 9, p. 094425-Article in journal (Refereed)
    Abstract [en]

    The total and magnetically resolved Compton profiles are analyzed within the combined density functional and dynamical mean-field theory for the transition-metal elements Fe and Ni. A rather good agreement between the measured and computed magnetic Compton profiles of Fe and Ni is obtained with the standard local spin-density approximation (LSDA). By including local but dynamic many-body correlations captured by dynamical mean-field theory (DMFT), the calculated magnetic Compton profile is further improved when compared with experiment. The second moment of the difference of the total Compton profiles between the LSDA and DMFT, along the same momentum direction, has been used to discuss the strength of electronic correlations in Fe and Ni.

  • 342. Chioncel, L.
    et al.
    Morari, C.
    Östlin, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Appelt, W. H.
    Droghetti, A.
    Radonjic, M.
    Rungger, I.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eckern, U.
    Postnikov, A. V.
    Transmission through correlated CunCoCun heterostructures2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 5, article id 054431Article in journal (Refereed)
    Abstract [en]

    We propose a method to compute the transmission through correlated heterostructures by combining density functional and many-body dynamical mean field theories. The heart of this combination consists in porting the many-body self-energy from an all electron basis into a pseudopotential localized atomic basis set. Using this combination we study the effects of local electronic interactions and finite temperatures on the transmission across the Cu4CoCu4 metallic heterostructure. It is shown that as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority-spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant d-electron contribution, as compared to the noncorrelated case in which the transport is dominated by s and p electrons.

  • 343. Chioncel, L.
    et al.
    Vitos, Levente
    KTH, Superseded Departments, Materials Science and Engineering.
    Abrikosov, I. A.
    Kollar, J.
    Katsnelson, M. I.
    Lichtenstein, A. I.
    Ab initio electronic structure calculations of correlated systems: An EMTO-DMFT approach2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 23Article in journal (Refereed)
    Abstract [en]

    We propose a self-consistent method for electronic structure calculations of correlated systems, which combines the local spin-density approximation (LSDA) and the dynamical mean field theory (DMFT). The LSDA part is based on the exact muffin-tin orbital approach, meanwhile the DMFT uses a perturbation scheme that includes the T matrix with fluctuation exchange approximation. The current LSDA+DMFT implementation fulfills both self-energy and charge self-consistency requirements. We present results on the electronic structure calculations for bulk 3d transition metals (Cr, Fe, and Ni) and for Fe/Cr magnetic multilayers. The latter demonstrates the importance of the correlation effects for the properties of magnetic heterostructures.

  • 344. Choi, Yun-Ki
    et al.
    Cho, Jun-Hyung
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bihlmayer, Gustav
    Weak antiferromagnetic superexchange interaction in fcc C60Hn2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 8, p. 081415-Article in journal (Refereed)
    Abstract [en]

    A recent density-functional calculation for fcc C60Hn (n = odd) [ K.W. Lee and C. E. Lee, Phys. Rev. Lett. 106, 166402 (2011)] proposed the existence of Stoner ferromagnetism based on an itinerant band model. However, our density-functional calculation shows that the antiferromagnetic (AFM) configuration is slightly more stable than the ferromagnetic (FM) one. This preference for antiferromagnetism over ferromagnetism is analogous to the case of a dimer (C60H)(2), where each C60H is spin polarized by an intramolecular exchange and the two magnetic moments are antiferromagnetically coupled with each other. The results demonstrate that the underlying mechanism of the magnetic order in fcc C60Hn is associated with the AFM superexchange between the magnetic moments created by H dopants.

  • 345.
    Choudhury, Debraj
    et al.
    Solid State and Structural Chemistry Unit, and Department of Physics, at Indian Institute of Science, Bangalore, Indien.
    Mukherjee, S
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, Indien.
    Mandal, P
    Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Indien.
    Sundaresan, A
    Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Indien.
    Waghamare, U V
    Theoretical Science Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Indien.
    Bhattacharjee, Satadeep
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sharma, Ajay
    Department of Physics, Indian Institute of Science, Bangalore, Indien.
    Bhat, S V
    Department of Physics, Indian Institute of Science, Bangalore, Indien.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Tuning of dielectric properties and magnetism of SrTiO3 by site-specific doping of Mn2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 12, p. 125124-Article in journal (Refereed)
    Abstract [en]

    Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO(3) has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d(0) state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems.

  • 346.
    Chung, S.
    et al.
    Department of Physics, Korea University.
    Lee, S.
    Chung, J. -H
    Yoo, T.
    Lee, H.
    Kirby, B.
    Liu, X.
    Furdyna, J. K.
    Giant magnetoresistance and long-range antiferromagnetic interlayer exchange coupling in (Ga,Mn)As/GaAs:Be multilayers2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 5Article in journal (Refereed)
    Abstract [en]

    We report the observation of the giant magnetoresistance effect in semiconductor-based GaMnAs/GaAs:Be multilayers. Clear transitions between low-field-high-resistance and high-field-low-resistance states are observed in selected samples with Be-doped nonmagnetic spacers. These samples also show negative coercive fields in their magnetic hysteresis and antiferromagnetic (AFM) splittings in polarized neutron reflectivity. Our data indicate that the AFM interlayer exchange couplings in this system occur over much longer periods than predicted by current theories, strongly suggesting that the coupling in III-V semiconductor-based magnetic multilayers is significantly longer ranged than in metallic systems. © 2010 The American Physical Society.

  • 347.
    Chung, S.
    et al.
    Department of Physics, Korea University.
    Lee, S.
    Liu, X.
    Furdyna, J. K.
    Magnetization reorientation in Gax Mn1-x As films: Planar Hall effect measurements2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 15Article in journal (Refereed)
    Abstract [en]

    The process of magnetization reorientation in a ferromagnetic semiconductor GaMnAs films was investigated using planar Hall effect measurements. In addition to the well-known two-step switching behavior that occurs during this process, we have observed two additional distinct features in field scan data of the planar Hall resistance (PHR). First, the region of the external field required to begin and complete the reorientation of magnetization from one easy axis to another strongly depends on the direction of the applied field. And second, the maximum amplitude of PHR is significantly reduced during magnetization reversal when the applied field is oriented near one of the easy axes of the GaMnAs film. We provide an explanation of these phenomena using the magnetic field dependence of the free-energy density and assuming the coexistence of multiple domains with three different directions of magnetization in the sample. © 2010 The American Physical Society.

  • 348. Chung, Sangwoo S.
    et al.
    Kakashvili, Paata
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Bolech, C. J.
    Numerical simulation of the Nernst effect in extreme type-II superconductors: A negative Nernst signal and its noise power spectra2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 13, p. 134525-Article in journal (Refereed)
    Abstract [en]

    Recently, different transport coefficients have been measured in high-T-c superconductors to pinpoint the nature of the pseudogap phase. In particular, the thermoelectric coefficients received considerable attention both theoretically and experimentally. We numerically simulate the Nernst effect in extreme type-II superconductors using the time-dependent Ginzburg-Landau equations. We report the sign reversal of the thermoelectric coefficient alpha(xy) at temperatures close to the mean-field transition temperature T-c(MF) (H), which qualitatively agrees with recent experiments on high-T-c materials. We also discuss the noise power spectrum of alpha(xy), which shows 1/f(beta) behavior. Based on this observation, we propose an experiment to distinguish among different regimes of vortex dynamics by measuring the noise correlations of the Nernst signal.

  • 349.
    Cobet, C
    et al.
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Esser, N
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Zetter, JT
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Richter, W
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Waltereit, P
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Brandt, O
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Ploog, KH
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Peters, S
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Edwards, NV
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Lindquist, OPA
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Cardona, M
    Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany Paul Drude Inst Festkorperelekt, D-10117 Berlin, Germany Sentech Instruments, D-12489 Berlin, Germany Linkoping Univ, IFM Mat Fys, S-85202 Linkoping, Sweden Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
    Optical properties of wurtzite AlxGa1-xN (x < 0.1) parallel and perpendicular to the c axis2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 16Article in journal (Refereed)
    Abstract [en]

    Measurements of the dielectric function components parallel and perpendicular to the optical axis of wurtzite GaN are presented. The results are obtained on a multilayer AlxGa1-xN / GaN film grown on gamma -LiAlO2 which exhibits a very small amount of Al (x<0.1) in the uppermost layer. We use the spectroscopic ellipsometry to determine (omega) around the interband critical points of GaN up to 9 eV. Since the optical axis of the films are parallel to the surface, a separation of the different epsilon components is possible. The line shape of the measured tensor components e(parallel to) and epsilon (perpendicular to) is in very good agreement with results of recently published band-structure calculations. By comparison with the calculations we assign structures in the dielectric function to critical points in the Brillouin zone. In addition, a comparison with similar spectra for CdS and CdSe is presented, together with a discussion of possible spin-orbit splitting effects.

  • 350.
    Colarieti-Tosti, Massimiliano
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Burkert, T.
    Department of Physics, Uppsala Universitet, Box 530, 751 21 Uppsala, Sweden.
    Eriksson, O.
    Department of Physics, Uppsala Universitet, Box 530, 751 21 Uppsala, Sweden.
    Nordstrom, L.
    Nordström, L., Department of Physics, Uppsala Universitet, Box 530, 751 21 Uppsala, Sweden.
    Brooks, M.S.S.
    Department of Physics, Uppsala Universitet, Box 530, 751 21 Uppsala, Sweden.
    Theory of the temperature dependence of the easy axis of magnetization in hcp Gd2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 9Article in journal (Refereed)
    Abstract [en]

    The magnetic anisotropy energy (MAE) of hcp Gd was calculated from first principles using the full-potential linear muffin-tin orbital method. It was found that the principal contributions to the MAE are the dipole-dipole interaction between the localized 4f spins and the spin-orbit interaction of the valence band states. The dipole contribution has the form 12K1d(1-cos2?), where ? is the angle between the magnetization direction and the c axis. The contribution of the spin-orbit interaction is shown to arise from the polarization of the conduction band that becomes exchange split due to exchange interaction with the localized 4f electrons. We argue that this leads to significant contributions from higher order anisotropy constants. An imposed reduced 4f moment leads to a repopulation of the electronic states at the Fermi level and a reduced exchange splitting of the valence states, which we demonstrate leads to a modification of the MAE. This modification is in qualitative agreement with the observed temperature dependence of the MAE. In addition, the dependence of the MAE on the ca ratio has been studied. © 2005 The American Physical Society.

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